Spark advance indicator



March 2,1943. B. H. SHORT 2,812,778

SPARK ADVANCE INDICATOR Filed Oct. 21, 1940 T6 SPARK PLU spmx 5 v k mekr' Ted/din, c 2 z 720 [fin/e) i NgENTQR i; Z AITORNEi Patented Mar. 2, 1943 SPARK ADVANCE mmcn'ron Brooks E. Short, Anderson, Ind, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application October 21, 1940, Serial No. 362,111

1 Claim.

This invention relates to devices for indicating spark advance for internal combustion engines.

The object of the invention is to provide electrically operated apparatus controlled by the sparking at a spark plug for causing a properly calibrated electric meter to read directly indegrees of spark advance. In the disclosed em bodiment of the present invention, this object is accomplished by providing a D. C. source of constant voltage which will cause a constant direct current to fiow through an electric current meter, by providing means automatically responsiveto sparking at an engine spark plug for establishing said current fiow and by providing means automatically responsive to top dead center position of the engine piston for interrupting said current flow. The meter will give a reading which varies in accordance with the duration of the current fiow; hence, the meter, when properly calibrated, will give a reading in degrees of spark advance ahead of top dead center.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred em bodiment of the present invention is clearly shown.

In the drawing:

Fig. 1 is a wiring diagram of the spark advance indicating apparatus.

Fig. 2 is a diagram of operation of the apparatus.

The current source of constant voltage is obtained by connecting, between the line wires l and ii of a 220 volt D. C. generator, a'voltage divider system comprising five type \IR 150voltage regulator tubes TU1, TUz, TU3, We and We connected in parallel, with a 100 ohm, 2 watt equalizing resistor in each tube circuit. These resistors are marked R1, R2, Ra, R4 and R5. The resulting parallel combination is connected in series with a 500 ohm, 20 watt fixed resistance Re which functions to absorb increased voltage. The operation of this combination is to maintain a constant voltage of 150 volts across the parallel combination, even when the load current varies between .15 amp. and .025 amp.

M is a D. C. milliammet'er originally intended to read from zero to 5 ma. It is calibrated to give a reading in degrees of spark advance.

The means which automatically establishes current flow through meter M at the instant of sparking is the thyratron TU-x which may be one engine piston" reaches top dead center.

of the type 2050 thyratrons. Tube TU-z is normally nonconducting since its grid is normally negatively biased by 3 volt battery BA1. At the instant of sparking in the #1 or any other engine cylinder, the grid bias of tube TUw becomes zero or positive thereby causing this tube to become conducting. It will remain conducting until its plate circuit is interrupted by rotary or slip ring switch SR. having a brush l2 and a conducting segment 53 of such length as to be in contact with brush I2 at the time of any possible sparking ahead of top dead center but to separate from the brush H2 at the instant the 0bviously segment I3 is rotated by any conveniently accessible engine driven part such as the crank shaft (not shown.) Rotary switch SR constitutes the means for causing tube 'I'Ua to interrupt the current flow to the meter M.

The voltage of #1 spark plug (or' any other. spark plug) is picked up by a very small capacity C1 (10 m. m. f., 30,000 v.) and is introduced through a variable resistance R1 (1000 ohm potentiometer or voltage divider) to the grid of an amplifier tube TUe which may be a type 6A6 or a 6N7. The output of amplifier TUB is coupled by transformer T1 (T84 D59 Thordarson) to the grid of thyratron TU'z. Although the initial lobe of the secondary voltage is negative with respect to ground, the impulse of voltage sent to the thyratron grid is positive. This impulse causes the thyratron grid to ionize the gas in tube Til-z so that plate conduction results. The current flow to meter immediately reaches maximum as soon as the spark plug fires and will continue at-that value indefinitely until the plate voltage is removed. The plate voltage is removed when the engine reaches top dead center thereby causing segment it to be separated irom brush it at that instant. The cur-' rent has been flowing at its constant peak a-b (see Fig. 2) throughout the time between the firing of the spark-plug and top dead center be set very accurately. This is accomplished by movingthe contact arms l4, l5 and N5 of usecal. switch SW1 from use positions (full lines in Fig. 1) to "cal (calibrate) positions H, I! and I6. (Dotted lines in Fig. 1), thereby caus-. ing zero voltage to be placed on the thyratron grid (which makes the thyratron conducting),

the slip 'ring switch S. R. to be shorted out, and

a resistance R10 (to suit the meter M) to be placed in shunt with the meter M.

" Resistance R (1500 ohms, 20 watt variable resistance) is adjusted until the meter M reads at a predetermined set position. That predetermined position or calibration mark on the meter dial has been obtained in the following manner. Let it be assumed, for example, that one wishes to use an ampere meter reading from zero to milliamperes on its scale to indicate, on thesame length of scale, zero to 80 of spark advance; This means that, when'the meter reads 80 spark advahce, the time integral of current ac (Fig. 2) over an engine cycle of 720 crank shaft degrees will be 5 m. a. The actual value of current ab (Fig. 2) flowing 'in the thyratron plate circuit during a spark advance period of 80 will be- 720/80 times 5 m. a.=45 m. a.

.In order to make this same 5 m. a. meter M give a reading of 45 m. a. a suitable resistance R10 is placed in shunt therewith. Electric current known to have the value of 45 m. a. is

the thyratron is adjusted until, the pointer of meter M coincides with the calibration mark indicating 45 m. a. current flow. Obviously, if one wished to use a 5 m. a. meter to give reading of 0 to 60 spark advance, the calibration mark would be 720/60X5 m. a. or 60 m. a.

The meter readings are proportioned to spark advance provided the current in the plate circuit remains constant. For example, if,the passage of 45 m. a. of current through the plate circuit during rapidly recurring periods of 80/720 of the engine cycle gives a read of the 5 m. a. or 80 spark advance on the meter dial, the passage of this same amount of current during rapidly recurring periods of 40/720 of the engine cycle will give a meter reading only one-half as great namely, 2.5 m. a. or 40 spark advance.

' Before beginning to take a series of readings of spark advance, the switch SW1 should be moved to calibrate position and the resistance Re should be adjusted if necessary so that the pointer of meter M will point to the calibration mark. Since the time of a previous use of the apparatus, conditions may have arisen to change the value of current in the plate circuit of the thyratron.

' fore given are as follows:

Resistance Ra-800 ohms, 10 watt (functions to put a negative bias on the grid of amplifier tube TUa).

Condensers Ca and C3 8 m. f.450 v. electrolytic condensers.

Battery AA-G volt battery (for heating tubes We and TU?) While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms mightbe adopted, all coming within the scope of the claim which follows.

What is claimed is as follows:

A spark advance indicating system comprising a D. C. ammeter constructed to give a current reading of zero to a: milliamperes and provided with a dial to give a spark advance reading of zero to 11 degrees, the reading of/y degrees corresponding to the reading of :c milliamperes, said dial bearing a calibration mark flow of milliamperes, z being the number of degrees of rotation of the engine crank shaft during the cycle of engine operation; a. resistance to be placed in shunt with the meter to obtain the calibration mark; a "use or operating circuit comprising acurrent source of constant potential, a thyratron tube for connecting the meter with the current source, means responsive to occurrence of sparking at an engine plug for causing the tube to become conducting and means responsive to top dead center of the engine piston associated with said spark plug for causing the meter to be disconnected from the current source; and a calibrating circuit comprising the current source, the tube, the meter, the resist-.

ance shunting the meter and a variable resistance for adjusting the continuous current flow through the plate cricuit of the tube so that the meter pointer will point to the meter calibration mark; and a circuit controller including a manually operated member having a calibrating position in which both of the aforesaid means are rendered non-operating and the meter and its shunt resistance are connected in paralleland both together in series with the tube' and current source and the tube grid is brought to zero voltage to make the tube conducting, and having a use positionin which both of the aforesaid means are rendered operating and the metershunt-resistance is open circuited.

BROOKS H. SHORT.

to indicate the 

